1. Field of the Invention
This invention relates to a photosensitive recording medium, and more particularly to a photosensitive recording medium on which image information is recorded by the action of light to form a color image.
2. Description of the Related Art
Photosensitive recording mediums are conventionally available which comprise a base material and held thereon photosensitive microcapsules comprised of a shell formed of a resin and, enclosed in the shell, a photosensitive material that undergoes polymerization upon exposure to light with a specific wavelength to harden or thicken (become viscous) and an image-forming agent.
Japanese Patent Application Laid-open No. 62-143044 also discloses a photosensitive recording medium comprising a base material and held thereon A) yellow color-forming microcapsules enclosing a yellow image-forming agent and a photosensitive material having a maximum hardening sensitivity to blue, which is complementary to yellow, i.e., having sensitivity to light of about 450 nm, B) magenta color-forming microcapsules enclosing a magenta image-forming agent and a photosensitive material having a maximum hardening sensitivity to green, which is complementary to magenta, i.e., having sensitivity to light of about 550 nm, and C) cyan color-forming microcapsules enclosing a cyan image-forming agent and a photosensitive material having a maximum hardening sensitivity to red, which is complementary to cyan, i.e., having sensitivity to light of about 650 nm.
Here, the image-forming agent is, specifically stated, a dye precursor. This dye precursor reacts with a color developer to form a color. In addition to those employing such a dye precursor, the present applicant has filed various patent applications relating to a photosensitive recording medium in which a dye or pigment which is colored in itself is used as the image-forming agent to make the color developer unnecessary.
The present applicant has also filed many patent applications relating to an image-forming apparatus such as a color copying machine of the type wherein, using such a photosensitive recording medium, the photosensitive recording medium is exposed to light transmitted through or reflected from a color original and thereafter an image-receiving sheet and the photosensitive recording medium are put together and pressed so that image-forming agents of microcapsules having not hardened are transferred to the image-receiving sheet to thereby form a full-color image on the image-receiving sheet.
In the above image-forming apparatus, a white-light source such as a halogen lamp is used, where the color original is irradiated with white light of the light source, and the photosensitive recording medium is exposed to the light transmitted therethrough or reflected therefrom, followed by pressing to effect development. Here, the light reflected from, e.g., red portions of the color original has a wavelength of 650 nm as a central wavelength, and hence the cyan color-forming microcapsules harden (to be more exact, photosensitive materials contained in the cyan color-forming microcapsules harden) but the yellow color-forming microcapsules and magenta color-forming microcapsules do not. Then, the image-receiving sheet and the photosensitive recording medium are put together and pressed, whereupon the cyan color-forming microcapsules having already hardened are not collapsed but the yellow color-forming microcapsules and magenta color-forming microcapsules having not hardened are collapsed, so that red color, which is a mixed color of yellow and magenta, is formed on the image-receiving sheet.
That is, in such a color copying machine, each color of the image-forming agent in the microcapsules stands complementary to the light giving a maximum value of photosensitivity of each photosensitive material. Color printers are also proposed in which the photosensitive recording medium is successively exposed to image information light having wavelengths of red, green and blue, using display devices that display images.
In this instance, the display devices include what is called Cathod Ray Tubes (CRT's), liquid-crystal display devices, fluorescent display tubes and light-emitting diodes (LEDs).
These display devices have their own characteristic features. The CRTs have a high emission luminance and are suited for exposure, but have the disadvantage that the apparatus must be made large in size. The liquid-crystal display devices are suited for making the apparatus small-sized, but have the disadvantage that they have no sufficiently high efficiency of light transmission and hence require long-time exposure because of an insufficient brightness in exposure.
Meanwhile, the LEDs and the fluorescent display tubes are self-emission type devices, and hence have a high emission luminance and also can make the apparatus smaller than the CRTs. Thus, they are considered preferable as exposure light sources.
Accordingly, such self-emission type light sources (e.g., LEDs) are usually used when photosensitive recording mediums are not exposed using the white light made incident on images of an original but exposed in accordance with image data (digital data) representing respective images of, e.g., a full color image separated into a red image, a green image and a blue image.
There is an important problem also when photosensitive recording mediums are exposed by means of such self-emission type display devices. That is, these display devices can not always emit exact light of red, green and blue, i.e., the light with wavelengths of 650 nm, 550 nm and 450 nm in order, and wavelengths around these. For example, in the case of LEDs, light-emitting devices of red, orange, yellow and green have been widely put into practical use and are available at moderate prices. However, devices that emit blue light with wavelength of about 450 nm have just began to be put into manufacture, and are of course so expensive that they are actually not feasible for practical use.
The fluorescent display tubes also have a similar problem. Although there are fluorescent materials that emit blue light with wavelength of about 450 nm, they have a much poorer emission efficiency for that color than other bluish green (about 505 nm) or green (about 520 nm), and hence they can not be used as exposure light sources.
Thus, it has been difficult to make up inexpensive printers by the use of conventional photosensitive recording mediums.